The species-time relationship (STR) is a macroecological pattern describing the increase in the observed species richness with the length of time censused. Understanding STRs is important for understanding the ecological processes underlying temporal turnover and species richness. However, accurate characterization of the STR has been hampered by the influence of sampling. I analyzed species-time relationships for 521 breeding bird survey communities. I used a model of sampling effects to demonstrate that the increase in richness was not due exclusively to sampling. I estimated the time scale at which ecological processes became dominant over sampling effects using a two-phase model combining a sampling phase and either a power function or logarithmic ecological phase. These two-phase models performed significantly better than sampling alone and better than simple power and logarithmic functions. Most communities’ dynamics were dominated by ecological processes over scales less than 5 years. This technique provides an example of a rigorous, quantitative approach to separating sampling from ecological processes.
White, E.P. 2004. Twophase speciestime relationships in North American land birds. Ecology Letters 7:329336.